There exist keys having one end secured to a yoke that is mounted between first and second cheeks of a casing so as to be capable of pivoting between a retracted position and an extended position about a pivot and a control pushbutton for controlling the pivoting of the key, which pivot and pushbutton are mounted in a bore of the yoke and respectively in a housing in the first cheek and in a housing in the second cheek. The control pushbutton is mounted in the bore to be constrained to pivot with the yoke and to be capable of sliding between a holding position in which it projects from the casing, in which position the pushbutton holds the yoke in the retracted position, and a position for releasing pivoting of the yoke. The pivot is indexed in pivoting within the housing of the first cheek so as to form a member for indexing a spring that is interposed between the pivot and the control pushbutton so as to urge the yoke resiliently towards the extended position and the control pushbutton towards the yoke-holding position.
In such keys, the pivot, the spring, and the control pushbutton are mounted in succession after the yoke has been put into place between the cheeks of the casing. The pivot is indexed as a result of an index projecting from the housing and engaging in a setback in the pivot. Unfortunately, it is found that if the key is subjected to an impact along the pivot axis of the yoke, e.g. because its user lets go of the key and it drops to the ground, then there is a risk of the pivot moving towards the pushbutton and thereby releasing the index from its setback. The spring then causes the pivot to pivot, thereby allow the spring to relax and thus preventing it from performing its function of returning the yoke to the extended position.